Telescopic boom angle control system



March 5, 1968 R. D. BROWNELL ET AL TELESCOPIVC BOOM ANGLE CONTROL SYSTEM 4 Sheets-Sheet 1 Filed March 1, 1967 March 5, 1968 R ow ET AL 3,371,799

TELESCOPIO BOOM ANGLE CONTROL SYSTEM Fild March 1, 1967 4 Sheets-Sheet 2 v 4 Sheets-Sheet 5 R. D. BROWNELL ET AL TELESCOPIC BOOM ANGLE CONTROL SYSTEM March 5, 1968 Filed March 1, 1967 4 Sheets-Sheet 4.

R. D. BROWNELL T AL TELESCOPIC BOOM ANGLE CONTROL SYSTEM *Q EW March 5, 1968 Filed March 1, 1967 United States Patent O 3,371,799 TELESCOPIC BOOM ANGLE CONTROL SYSTEM Roy D. Brownell, Aurora, and Granville Woolman, Naperville, Ill., assignors to Baldwiu-Lirna-Harnilton Corporation, Chicago, Ill., a corporation of Delaware Filed Mar. 1, 1967, Ser. No. 619,628 12 Claims. (Cl. 212-35) ABSTRACT OF THE DISCLOSURE A boom angle control system for a cable supported telescopic boom section employing boom angle sensing mechanism operative to control the effective length of supporting cable to maintain a preselected boom angle as the telescopic boom section is extended or retracted by independent power means.

Background of the invention The present invention relates generally to vertically swingable crane booms and more particularly concerns automatic angle control arrangements for cable supported telescopic crane booms.

Vertically swingable crane booms are generally mounted on the crane frame either in a cantilever fashion or they are supported by a cable secured to a gantry mechanism on the crane frame. In the cantilever arrangement, one or more power units between the boom and the frame are used to change the boom angle. The boom may also be telescopic and with the cantilever arrangement extension and retraction of the boom does not alter the boom angle. However, the length of the cantilever boom is limited since this supporting arrangement requires a boom having a large cross section if undue deflection is to be avoided and, of course, in a telescopic boom this problem is increased with each additional telescopic section.

In the cable and gantry support arrangement the boom angle is changed by paying out or drawing in the cable. With this arrangement the boom construction can be made substantially lighter since the outer portion of the boom is also supported. Although cable supported booms may also be telescopic, they are generally operated at a fixed length since extension and retraction of the boom also changes the boom angle and this is usually not desirable during normal operation. In some instances the operators controls are so arranged that it is possible to simultaneously adjust the boom angle as it is being telescoped, but this requires considerable skill on the part of the operator and also it restricts his ability to perform other functions. In other instances, namely where the boom is supported and also telescoped through the use of cables, it has been possible to interconnect the cable mechanisms in such a way that the different cables are simultaneously adjusted. However, these arrangements are not suitable for use on cable supported telescopic boom cranes in which the boom is extended and retracted by other power means.

Summary the invention It is the primary aim of the present invention to provide a control system for a cable supported telescopic boom in which the boom is extended and retracted by independent power means and which includes means for sensing the tendency of the boom to change angle as it is extended and retracted and which automatically adjusts the supporting cable to compensate for this tendency. A more specific object is to provide a hydraulically powered winch for the boom support cable and to arrange the boom angle sensing means to control a valve for reversibly actuating the the cable winch to maintain a preselected boom angle as the boom is telescoped.

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Another object is to provide a control system as described above which is arranged to permit the crane op erator to rapidly move the boom angle control element to a preselected position and through the-follow-up operation of the boom angle sensing means be assured that the boom will automatically move to the angle corresponding to this setting without further attention of the operator. It is also an object of the invention to provide a control system of the foregoing type that is simple and reliable and which may be easily installed on new or existing cranes of a wide variety of types and sizes.

Brief description of the drawings FIG. 1 is a side elevation View, with certain portions broken away, of a cable supported, telescopic boom crane embodying the control system of the present invention;

FIG. 2 is a fragmentary view of a portion of one form of the angle sensing mechanism of the invention;

FIG. 3 is a schematic circuit diagram for the control system associated with the mechanism shown in FIG. 2;

FIG. 4 is a fragmentary view of a portion of a modified form of the angle sensing mechanism of the invention;

FIG. 5 is a schematic circuit diagram for the control system associated with the mechanism shown in FIG. 4;

FIG. 6 is a fragmentary view of a portion of another modified form of the angle sensing mechanism of the invention; and

FIG. 7 is a schematic circuit diagram for the control system associated with the mechanism shown in FIG. 6.

While the invention will be described in connection with certain preferred embodiments, it will be understood that we do not intend to limit the invention to those embodiments. On the contrary, we intend to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Description of the preferred embodiments Turning now to the drawings, there is shown in FIG. 1 a self-propelled crane indicated generally at 10. The crane 10 is provided with a chassis 11 supported by ground engaging wheels 12 and having a forward operators cab 13 in which the controls for steering and propelling the crane are located. A crane support frame 14 is also mounted on the chassis 11 by means of a turntable 15 which permits the crane frame to rotate in either direction about the vertical axis of the turntable. The crane frame is covered by an enclosure 16 in which the power unit of the crane and the crane operating controls are located.

A telescopic boom 17 is pivotally mounted at 18 on the crane frame 14- for vertically swinging movement. The boom 17 of the illustrated embodiment includes a base section 19, an intermediate extensible section 20 which is extendible and retractable by power means 21 and a tip section 22 which may also be extendible and retractable by power means (not shown). The' tip section 22 is also provided with a tip block 23 which journals a pair of pulleys 24 and 25 over which the load line 26 is trained. The rear end of the load line is wound on a power winch 27 and the forward end carries a hook block 28 for raising and lowering a load upon selective actuation of the load winch 27.

For supporting and changing the vertical angle of the boom 17 with respect to the crane frame 14, a supporting cable 30 is wound on a power winch 31 and coupled to the boom 17. The cable 30 is trained over a pulley 32 journalled by a lower gantry support 33 and, in order to provide sufficient strength for supporting the boom, the cable makes several reaches between a pulley 34 journalled at the upper end of the extensible section 20 and an upper gantry support 35 secured to the crane frame 14. It will be 3 understood that as the cable 36 is wound on the winch 31 the boom 17 swings upwardly and, conversely, as the cable is paid out the boom swings downwardly about pivot 18.

As shown in FIG. 3, the winch 31 is driven by a hydraulic motor 36 through a gear box 37. Hydraulic fluid for the motor 36 is supplied from a reservoir 38 by a pump 39. A four-way valve 40 selectively regulates the flow of hydraulic fluid from the pump to the motor and back to the reservoir through suitable hydraulic supplyreturn lines 41, 42, 43 and 44. A drain line 45 is also provided from the motor 36 to return any leakage to the reservoir 33. A manual control element 47 is operatively connected to the valve 40 as will be hereafter explained in more detail to permit the operator to change the boom angle.

To prevent unwinding of the cable 30 from the winch 31 when the motor 36 is not operated, a spring loaded brake illustrated generally at 48 is interposed between the motor 36 and gear box 37. The brake 48 is automatically disengaged by a hydraulic actuator 49 incident to operation of the winch motor in either direction. The actuator 49 is supplied hydraulic fluid through a conduit 50 and a pressure responsive valve 51 from whichever one of lines 42 or 43 is pressurized. When the motor 36 is not operated a check valve 52 in conduit 50 dumps fluid from the actuator 49 through a drain line 53 and drain line 45 to the reservoir 38. To provide more accurate control and dynamic braking of the motor 36 when the boom is lowered a restrictor valve 54 is desirably installed in line 43 between the motor 36 and control valve 40.

In the illustrated embodiments the power means 21 for extending and retracting the intermediate boom section with respect to the boom base section 19 are in the form of a pair of two stage single acting hydraulic cylinders.

prevents undesirable retraction of the cylinders 21 which could otherwise result from leakage in valve 57. The check valve 62 is preferably pilot operated and in the illustrated embodiments is automatically supplied with pilot pressure through line 63 when the main valve 57 is operated to exhaust fluid from the cylinders 21 through line 60 and return line 44 to the reservoir 38. For controlling the maximum rate that the boom 17 can retract even when subjected to a heavy load, a one way flow regulator or restrictor valve 64 is preferably installed in supply-return line 60.

When the intermediate section 20 of the boom 17 is extended by the hydraulic power means 21, the boom tends to rise unless additional supporting cable is unwound from the winch 31. Conversely, when the intermediate extensible section 20 is retracted, the boom 17 tends to lower unless a portion of the cable 30 is wound onto the winch 31.

In accordance with the present invention means are provided for sensing the tendency of the boom 17 to change its angle with respect to the crane frame 14 as the boom is extended or retracted and for automatically actuating the boom winch 31 to selectively wind or unwind the cable 30 in order to maintain a preselected boom angle. For this purpose boom angle sensing means is arranged to operate the boom winch valve in order to compensate for the tendency of the boom to change its angle as the intermediate boom section 26 is extended or retracted by the power means 21.

As shown in FIGS. 2 and 3, the boom angle sensing and compensating means comprises a mechanical linkage 65 interconnecting the boom 17 and boom angle control A], lever 47 with the boom winch control valve 40. The linkage 65 includes link 66 pivotably connected intermediate its ends to the valve spool 67. One end of the link 66 is connected to the boom 17 eccentric of the pivot 18 by an angle sensing link 68. The other end of the link 66 is connected to the control lever 47 by a control link 69. Movement of either the angle sensing link 68 or control link 69 causes pivotal movement of the valve operating link 66 and consequent movement of the valve spool 67 whereby the valve 40 actuates the winch motor 36.

Selection of the boom angle with respect to the crane frame 14 may be made by the operator through movements of the boom angle control lever 47, which is preferably of the self-locking or non-back driving type. Upon movement of the lever 47, the link 69 causes the lever 66 to shift the valve spool 67 thereby operating the winch motor 36. As seen in the drawings, movement of the lever 47 to the left operates the motor 35 to pay out cable 30 from the winch 31 and lower the boom 17. Movement of the lever 47 to the right causes the boom to rise.

When the boom 17 tends to rise due to extension of section 20 by the power means 21, the boom angle sensing link 68 moves to pivot link 66 in a counterclockwise direction and actuate the valve 40 for supplying fluid to the winch motor 36 to pay out the cable 30. The winch 31 continues to pay out cable as long as the link 68 senses the tendency of the boom 17 to rise. Similarly, if the boom tends to lower due to retraction of the intermediate section 26 the angle sensing link 68 moves to cause the valve operating lever 66 to actuate the valve 40 in a winch raising direction and compensates for this tendency.'In this way the boom angle preselected by the operator through movement of the lever 47 may be maintained substantially constant as the intermediate boom section 20 is extended or retracted by the hydraulic cylinders 21.

Provision is also made to permit the operator to quickly select a new boom angle. For this purpose the control link 69 preferably comprises a spring biased lost motion link which allows the operator to rapidly move the lever 47 to a new position and through the follow-up operation of the boom angle sensing link 68 be assured that the boom 17 will automatically move to the newly selected angle without further attention of the operator.

As shown in FIG. 2 the link 69 carries a compression spring 70 between a pair of locating washers or collars 71 and 72 which abut respective annular shoulders 73 and 74 in a spring housing 75 coupled to the control lever 47. Thus, movement of the housing 75 by the lever 47 in either direction serves to compress the spring 70 and transmit a biasing force to the valve operating lever 66. As the boom 17 changes its angle due to operation of the valve 40, the angle sensing link 68 moves the other end of the valve operating link 66 and gradually unbiases the spring 70 until the preselected boom angle has been established.

Turning now to FIGS. 4 and 5 there is illustrated a modified angle sensing and compensating means comprising a hydraulic pilot system 76 interconnecting the boom 17 and boom angle control lever 47 with a pilot type boom winch control valve 40a. It Will be noted that the remaining portions of the control system are similar to that shown in FIGS. 2 and 3 and therefore have been similarly numbered.

The illustrated pilot system 76 includes a pair of balanced displacement type double acting hydraulic cylinders '77 and 78, enclosing pistons 79 and 80, one connected to the boom 17 eccentrically of the pivot 18 and the other connected to the control lever 47. Desirably the latter connection is by means of a spring biased lost motion linkage 81 similar to the linkage 69 in FIG. 2 in order to provide for rapid movement of the control lever 47 for quickly preselecting a new boom angle. The opposite ends of the cylinders 77 and 78 are interconnected by pilot lines 82 and 83, respectively, and these pilot lines, in turn, are

coupled to opposite sides of the pilot section of control valve 40a.

When the boom angle control lever 47 is moved to the left, as seen in FIG. 4, piston 80 is urged to the right creating an increase in pressure in the right end of cylinder 78. This increased pressure is communicated through pilot line 83 to the left side of the pilot operated valve 40a opening the valve for operating the motor 36 in a winch lowering direction. Operation of the winch motor 36 continues until sufiicient cable 30 has been paid out to lower the boom 17 causing movement of the piston 79 in cylinder 77 to the left thereby equalizing the pressure in pilot line 83 and discontinuing operation of the valve 40a. Movement of the control lever to the right pressurizes pilot line 82 and causes the boom to rise until the pressure is again equalized by the follow-up movement of piston 79 in the angle sensing cylinder 77.

Any tendency of the boom 17 to change its angle upon extension or retraction of the section 20 causes a pressure differential in pilot lines 82 and 83 due to movement of piston 79 in the angle sensing cylinder 77. This pressure dilferential is communicated to the pilot section of valve 40a and causes the valve to operate the winch motor 36. Operation of the Winch motor continues untilsufficient cable is paid out or taken up to compensate for the tendency of the boom to change angle whereupon the pressure in lines 82 and 83 is again equalized and valve operation is terminated. The use of balanced displacement type double acting cylinders 77 and 78 permits quick and uniform response of the pilot control system which is thereby effective to maintain the boom substantially at its preselected angle as it is extended or retracted. Moreover, as pointed out above the spring biased lost motion connection 81 permits the operator to rapidly move control lever 47 to quickly select a new boom angle and be assured that the boom will move to this selected angle without further attention of the operator.

Another embodiment of the angle sensing and compensating means of the present invention is illustrated in FIGS. 6 and 7. As shown here an electro-hydraulic control system 85 is employed to control the boom angle and to maintain the preselected boom angle substantially constant as the intermediate boom section 20 is extended or retracted. In this embodiment an electro-hydraulic pilot valve 86 is coupled to the pilot section of valve 40a through pilot lines 87 and 88. A small pilot pump 84 supplies fluid to the pilot valve 86 through line 84a and unless the valve is operated the fluid returns to the reservoir through lines 84b.

Actuation of the electro-hydraulic pilot valve 86 is controlled by a differential electrical potential across input terminals 89 and 90 of a coil 91 which controls movement of the valve spool (not shown). The variable output terminals of an angle selection potentiometer 92 and a boom angle sensing potentiometer 93 are respectively connected to terminals 89 and 90 by wires 94 and 95. A source of direct current is connected in parallel to the input terminals of potentiometers 92 and 93 by wires 96 and 97.

When both the boom angle selection potentiometer 92 and boom angle sensing potentiometer 93 are in like relative positions there is no differential potential across the valve coil terminals 89 and 90 and thus no movement of the valve spool and no output through pilot lines 87 and 88. By moving control lever 47 the resistance of potentiometer 92 is changed and a differential potential across terminals 89 and 90 is established. This causes operation of electro-hydraulic valve 86 and a consequent pressure dilferential in pilot lines 87 and 88 for operating valve 40a and actuation of the winch motor 36. The winch motor continues to operate thereby changing the boom angle until movement of the angle sensing potentiometer 93 is such to eliminate the differential potential across terminals 89 and 90.

The tendency of the boom to rise or lower incident to extension or retraction is also effective to create a differential potential across terminals 89 and 90. In this case the pilot valve 86 is operated producing a diiferential pressure in lines 87 and 88 and the winch motor is thereby operated by valve 40a until the cable length is altered sufficiently to return the angle sensing potentiometer 93 to its original position. This, of course, eliminates the differential potential across terminals 89 and 90 and the control system is again in an equilibrium condition.

From the foregoing it will be appreciated that each of the illustrated embodiments provides means for the operator to select and change the boom angle and means for sensing the tendency of the boom angle to change incident to extension or retraction of the boom section 20. Furthermore, the boom angle sensing means is operative to actuate the boom winch and wind or unwind the cable 30 to maintain the preselected boom angle as the boom is extended or retracted.

We claim as our invention:

1. A control system for a telescopic boom crane having a frame with the boom base section pivotably mounted thereon for vertically swinging movement and a cable connected to an extensible boom section for supporting and changing the vertical angle of the boom relative to the frame comprising, in combination, means for extending and retracting said extensible section relative to said base section, means for sensing changes in said boom angle as said extensible section is extended and retracted, power winch means for selectively winding and unwinding said cable for changing said boom angle independent from operation of said extending and retracting means, and angle adjusting means interconnecting said angle sensing means and said winch means for automatically actuating said winch means to maintain a preselected boom angle as said extensible section is extended and retracted.

2. A control system as defined in claim 1 wherein said winch means is hydraulically controlled and said angle adjusting means includes a valve operable by said angle sensing means for controlling the supply and discharge of hydraulic fluid to and from said winch control means.

3. A control system as defined in claim 2 including, a manually movable control element for independently operating said valve to selectively control said boom angle, said control element and said angle sensing means each being connected to said valve, whereby said valve is operable by said control element to select boom angle, and said valve is operable by said angle sensing means to maintain said selected boom angle as said extensible section is extended and retracted.

4. A control system as defined in claim 3 wherein resilient means are provided for permitting rapid selection of a new boom angle including a spring biased upon rapid movement of said control element in either direction to select a new boom angle, said valve being operable by the biasing force exerted by said spring to change the previous boom angle, and means including said angle sensing means for unbiasing said spring as said boom is moved to said new angle.

5. A control system as defined by claim 3 wherein said valve is operated :by a mechanical linkage interconnecting said control element and said angle sensing means with said valve.

6. A control system as defined by claim 5 wherein resilient means are provided for permitting rapid selection of a new boom angle including a spring connection between said control element and said linkage, said spring being biased upon rapid movement of said control elemerit in either direction to select a new boom angle, said spring when biased operable to exert a force on and move said linkage in one direction and actuate said valve to change the previous boom angle, and said angle sensing means operable to move said linkage and unbias said spring as said boom is moved to said new angle.

7. A control system as defined by claim 3 wherein said valve is pilot operated and said control element and said angle sensing means are interconnected with said valve by means of a pilot control circuit.

8. A control system as defined by claim 7 wherein said pilot control circuit includes a balanced displacement type double acting hydraulic cylinder and piston arrangement connected to each of said control element and angle sensing means with the opposite ends of said cylinders being hydraulically interconnected and coupled to opposite sides of said pilot operated valve whereby relative movement of either of said pistons in its cylinder produces a differential pressure signal and operates said valve to change said boom angle until said differential pressure signal is compensated for by subsequent movement of one of said pistons in its cylinder.

9. A control system as defined by claim 8 including a spring connection between said control element and its hydraulic cylinder and piston arrangement, said spring being biased upon rapid movement of said control element in either direction to select a new boom angle, said spring when biased operable to exert a force on and move the piston in said cylinder to produce a differential pressure signal for operating said valve to change the previous boom angle, and said angle sensing means operable to move the piston in its cylinder thereby reducing said differential pressure signal and unbiasing said Spring as said boom is moved to said new angle.

10. A control system as defined by claim 7 wherein said pilot control circuit includes a source of pilot supply pressure, an electrohydrauldic pilot control valve interposed between said source and said pilot operated valve, and electrical circuit means connected to said electrohydraulic pilot control valve and operative to produce a differential potential across said pilot control valve whereby a differential pilot pressure signal is communicated to said pilot operated valve.

11. A control system as defined by claim 10 wherein said electrical circuit means includes a pair of variable potentiometers respectively coupled to and operable by said control element and said angle sensing means.

12. A control system as defined by claim 11 wherein said control element is pivotably mounted on a portion of said crane frame and one of said potentiometers is coaxially disposed with respect to said pivotal mounting and the other of said potentiometers is operatively disposed adjacent the pivotal mounting of said boom base section.

References Cited UNITED STATES PATENTS 2,787,383 4/1957 Antos 212-35 FOREIGN PATENTS 1,210,405 3/1960 France.

EVON C. BLUNK, Primary Examiner.

H. C. HORNSBY, Assistant Examiner. 

